The present invention is directed to an electroplating apparatus for plate-shaped workpieces, particularly printed circuit boards, which workpieces are conducted through an electrolyte solution in a horizontal path for the application of a metal thereto.
An electroplating apparatus for electroplating plateshaped workpieces moving in a horizontal path is disclosed in U.S. Pat. No. 4,385,967, whose disclosure is incorporated herein by reference thereto, and which was the basis of German DE-A 32 36 545. In the apparatus of this patent, plate-shaped workpieces are conducted through an electrolyte solution in a horizontal path. Feed of the workpieces occurs by driven contact wheels that are arranged at one side in the treatment cell and also simultaneously serves as a contacting mechanism for the cathodic contacting of the workpieces. Shieldings extending in the throughput direction and having sealing ledges press against the respective workpieces are provided for protecting the contact wheels against the electrolyte solution. A special guide fastener, which is arranged at the side of the treatment cell opposite to the contact wheels, is arranged for guiding and holding the workpieces.
In the electroplating apparatus described above, the employment of the sealing ledges cannot adequately prevent the access of electrolyte solution to the lateral contacting region of the workpiece and to the contact wheels. As a consequence of these incomplete seals, spongy metal depositions occur in the contact region, a rapid deterioration of the rolling contact occurs and unfavorable distribution of the layer thicknesses of the electrodeposited layers or, respectively, a great scatter of the layer of thicknesses, will occur.
U.S. Pat. No. 4,776,939, whose disclosure is incorporated herein by reference thereto and which was based on German Application No. 36 24 481, discloses an electroplating apparatus wherein the conveyor means is constructed as an endless circulating, driven row of individual conveyor elements that retain the lateral edge of the plate-shaped workpiece and move in a conveying direction. At the beginning of the conveying path, means are provided to create a grasping of the plate-shaped workpiece by the conveyor elements, and at the end of the conveyor path, means are provided to create a release of the plate-shaped workpiece by the conveyor elements which are being passed through the electrolysis chamber. Apart from the beginning of the grasping and the beginning of the releasing, no relative movement between the conveyor element and the workpiece edges will occur so that the wear phenomena or, respectively, abrasion phenomena of the conveyor elements is avoided. The conveyor elements can, thus, also simultaneously serve for supplying power to the plate-shaped workpiece.
U.S. Pat. No. 4,755,271, whose disclosure is incorporated herein by reference thereto and which is based on the same German Application as European Application A-0 254 962, discloses another type of electroplating apparatus of the above-mentioned type, wherein the contacting mechanism is formed by forceps-shaped contact clamps laterally displaceable together with the workpiece. These clamps are placed on an endless drive which, preferably, serves as a displaceable carrier of the contact clamps. The contact clamps also simultaneously serve as conveyor elements for the throughput of the workpiece. The contact clamps are shielded from the access of the electrolyte solution by a seal laterally extending in the throughput direction and resiliently pressing against the respective workpiece.